1. Field of the Invention
The present invention relates to a control system for performing control of an engine, and more particularly to an engine control system capable of controlling torque of an onboard engine with high accuracy.
2. Description of the Related Art
Recently, there has been a demand for higher accuracy in engine torque control against the background of a trend toward electronic driving (so-called X By Wire) of engine peripheral equipment, hybrid driving of a vehicle in combination with a motor, and so on. Engine torque is controlled using, as main control inputs, an intake air amount (fuel supply amount depending on it), an air/fuel ratio (fuel supply amount depending on it), and ignition timing. Devices (such as an electronically controlled throttle valve, a fuel injection valve, and an ignition plug) for controlling the control inputs inevitably undergo variations in torque sensitivity with respect to the control inputs due to variations in initial performance caused by differences among engines (individual differences), variations caused by performance changes with time, variations caused by environmental changes, etc. Also, it is an actual situation that, even when indicated torque is highly accurately controlled by controlling the intake air amount, the air/fuel ratio, and the ignition timing with high accuracy, axial torque cannot be always controlled with the desired high accuracy because internal loss (torque) of the engine is decided depending on many factors.
On the other hand, an engine torque system includes a transfer characteristic (delay) in a conversion path from the main control inputs, i.e., the intake air amount, the air/fuel ratio, and the ignition timing, to the torque, i.e., a control variable. To realize a torque control system with good response, therefore, the torque control system has to be constructed in consideration of such a transmission characteristic (delay).
Thus, in order to realize the engine torque control with high accuracy, it is required to construct a torque control system having not only robustness against the variations caused by the individual differences, the changes with time, the environmental changes, and the internal loss, but also high response in consideration of the transmission characteristic (delay) in the engine torque system.